1. Field of the Invention
The present invention relates to a method of producing an electrical double layer capacitor and particularly to a method of producing an electrical double layer capacitor including a step of cutting such a capacitor into a desired shape by means of a die or the like.
2. Description of the Prior Art
FIG. 1 is a cross-sectional view of a structure of an electrical double layer capacitor which is improved by the present invention. The electrical double layer capacitor as shown here comprises a pair of polarization electrodes 2 separated by a separator 1 comprised of an electronically non-conductive porous polyolefin material. The polarization electrodes are formed mainly out of activated charcoal and a dilute sulfuric acid electrolyte. A pair of current collecting electrodes 3 are put into contact with the respective polarization electrodes 2 to act as terminals of the electrical double layer capacitor. The current collecting electrodes 3 are comprised, for example, of a conductive rubber sheet.
A pair of insulator members 4 are used to maintain the above-mentioned separator 1, the polarization electrodes 2, and the current collecting electrodes 3 in the desired arrangement. That is, each of the insulator members 4 form an opening 5 for receiving the polarization electrode 2, and the separator 1 is sandwiched between and fixed to the insulator members 4. Then the current collecting electrodes 3 are bonded to the periphery of the thus formed structure.
In producing electrical double layer capacitors having such a shape as shown in FIG. 1, conventionally, means such as a metal die have been used for cutting the periphery of a semi-processed structure in an intermediate step to obtain such an electrical double layer capacitor. Therefore, there was a tendency that the conductive resin material forming the current collecting electrode 3 was smeared on the end surface of the periphery of the insulator member 4 after the cutting step, as shown in FIG. 2 as the smeared portion 6. There was a disadvantage, therefore, that such a smeared portion 6 of the conductive resin material caused a short-circuit between the upper and lower current collecting electrodes 3, as shown in FIG. 2. This increases the leakage current, reduces the breakdown voltage and insulation capacity of the device.
An object of the present invention is therefore to provide a method of producing an electrical double layer capacitor in which, even if such a smearing of the current carrying electrodes occurs, it has no effect on the performance of the device.